| Cylindrical materials--such as bars, pipes, and axle—have contributed enormously to the national economy and defense construction. Furthermore, nondestructive testing has become indispensable to ensure cylindrical materials' quality and utility. Though there are many ways to conduct nondestructive testing, ultrasonic nondestructive testing appears to improve ceaselessly in reliability. The security, the applicability, the richness of information, and the convenience of integrating with informational technology of ultrasonic nondestructive testing exceed that of other types of nondestructive testing. Thus, ultrasonic nondestructive testing is said to be the most applicable testing which has the greatest potential to be yet developed. However, as the industry has been expanding rapidly, the original ultrasonic nondestructive testing can hardly meet the demand for higher accuracy, hence cannot fulfill the requirements to monitor material's quality.Therefore, it is necessary to integrate mechatronics with phased array ultrasonic imaging. This integration allows real-time automatic cylindrical material testing, hence enhancing its accuracy and efficiency. On the other hand, due to the complexity of the transmission of ultrasonic waves,the acoustic signal may be influenced by diffraction, reflection, pulse spatial response, acoustic attenuation, and many other acoustic effects, the imaging resolution of ultrasonic technology is negatively affected in a large scale. At present, though some studies have suggested applicable arithmetic and theories, but most of them are based on the cylindrical coordinate system. However,this system becomes less useful when being applied to helical scanning. This lack of theories on the field of helical scanning hinders the development of the algorithm in image resolution. Based on these backgrounds, this study, along with National Natural Science Foundation of China(No.51675480), develops the technology of real-time phased array ultrasonic imaging in cylindrical materials testing. While analyzing the status and future trend of ultrasonic nondestructive testing, this study focuses on the synthesis of sound field, sparse deconvolution and frequency-domain synthetic aperture focusing technique for complex layered surfaces and helical scanning. The suggested method can fill in the gap for having a real-time qualified ultrasonic testing.At the same time, a real-time testing system is developed to verify the applicability and efficiency of the theories proposed by this study.Chapter 1 describes the significance of cylindrical material to the national economy and defense construction. While explaining the importance to conduct this study,this chapter also points out the challenges that phased array ultrasonic imaging is facing. This chapter analyzes the current theories for solving these problems and the future trends of the technology. In addition, it provides an outline for the paper.Chapter 2 starts with the study of the basic theory of phased array ultrasonic imaging. This theory finds solution via the wave equation under the cylindrical and helical coordinates to confirm and actualize the wave transmission inside the cylindrical materials. This chapter also analyzes the characteristics of phased array ultrasonic transducer and the synthesis of sonic beam. This chapter further discusses the theory of compound imaging.Chapter 3 suggests the sparse blind deconvolution of phased array ultrasonic imaging.Building up on the deconvolution model and using OMP to realize the sparse deconvolution, it estimates the influence of impulse over functional spectrum through asymmetrical Gaussian model.It realizes the operation of blind deconvolution via circular iteration to eventually achieve the purpose of improving the time resolution of ultrasonic imaging. The result of the experiment shows that this technique is very effective when the change in echo is large. This technique is efficient in ameliorating the time resolution of ultrasonic imaging and in erasing the blind spots while checking overlaid materials.Chapter 4 suggests a phased array ultrasonic frequency-domain synthetic aperture focusing technique under the circumferential scanning mode. Using both the solution found under cylindrical coordinates and frequency expression of signal model rebuilt by Fourier transform, to speculate the formula for cylindrical sound field reconstruction under the conditions on explosion reflection model. Based on this formula, we may reconstruct the interested areas on a cylindrical surface to achieve a higher spatial resolution of phased array ultrasonic imaging in circumferential testing. Both the stimulation and experiment show that this method is effective in improving the spatial resolution of ultrasonic imaging.Chapter 5 suggests a phased array ultrasonic frequency-domain synthetic aperture focusing technique under the helical scanning mode. Using both the solution found under helical coordinates and frequency expression of testing signal model rebuilt by Fourier transform,to speculate the formula for cylindrical sound field reconstruction under the conditions for explosion reflection model. Based on this formula, we may reconstruct the interested areas on a helical surface to achieve a higher spatial resolution of phased array ultrasonic imaging in helical testing. Both the stimulation and experiment show that this method is effective in improving the spatial resolution of ultrasonic imaging.Chapter 6 suggests the phased array ultrasonic frequency-domain synthetic aperture focusing technique for complex cylindrical structures. By combing two phased array ultrasonic frequency-domain synthetic aperture focusing technique mentioned above, we may construct an all-purposed phased array ultrasonic frequency-domain synthetic aperture focusing technique. This technique involves Step-split Fourier to adapt to the irregular stratification to eventually achieve a higher spatial resolution of phased array ultrasonic imaging while analyzing complex cylindrical structures. The result from the experiment shows that this expanded frequency-domain synthetic aperture focusing technique also keeps a high spatial resolution when analyzing complex cylindrical structures.Chapter 7 studies the applicability of real-time phased array ultrasonic imaging based on the results from the research described in the chapters above. After completing the general design,we used PXI emulate system to develop a set of 32/182 phased array board and integrated it with mechatronics to make a machine for cylindrical materials' real-time phased array ultrasonic testing.The newly developed equipment was tested with seamless steel tubes. The result shows that the system successfully implements the real-time phased array ultrasonic imaging and verifies the applicability and effectiveness of the theories and techniques discussed in this study.Chapter 8 concludes the new developments resulted from this study and discusses more possibility that can be explored in the future. |
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